JPH0755561A - Photosensor - Google Patents

Abstract

PURPOSE:To provide a photosensor in which an S/N ratio can be improved with a simple structure in the photosensor for detecting a narrow band light while the senser is moving. CONSTITUTION:A detecting position of a photodetector 5 is controlled by rotatably holding an interference filter 3 so provided as to cut a light having an unnecessary band between a condensing lens 2 and the photodetector 5 in a frame 6 fixed to the photodetector 5, driving a piezoelectric element 7 provided between the frame 6 and the filter 3 according to a drive signal from a driving circuit 8 thereby to rotate the filter 3, providing an angle to the photodetector 5, and refracting an incident light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector, and more particularly to a photodetector for detecting narrow band light while moving.

In recent years, remote sensing has been carried out by using artificial satellites or the like to perform ultra-high range exploration from a high sky by utilizing the phenomenon of reflection / radiation of light in the visible range, near infrared range, far infrared range, microwave range, etc. Has been.

The photodetector used in such remote sensing is required to detect a narrow optical band and to have high spatial resolution without deterioration of the SN (signal / noise) ratio.

[0004]

2. Description of the Related Art FIG. 5 is a diagram for explaining remote sensing by an artificial satellite. In the figure, 31 indicates an artificial satellite. The artificial satellite 31 is equipped with a light detection device and the like, and for example, the sky above about 800 km is about 18 km / s with respect to the ground 32.
While flying at a speed of, the image of the ground 32 can be captured as a belt-shaped region 33 parallel to the flight direction (direction of arrow C ₂ ),
Send to the ground.

In a photodetector mounted on an artificial satellite or the like for detecting light while moving, assuming that the signal integration time is t _int , the light receiving element area is A, and the amount of light incident per unit area is φ, the SN ratio S / The theoretical limit of N is generally expressed by S / N = √ (φ · A · t _int ) (1).

At this time, the improvement of the spatial resolution means that the signal integration time t _int and the light receiving element area A become smaller, and the narrowing of the optical band means that φ becomes smaller. ) Further improvement of spatial resolution and narrowing of optical band lead to deterioration of S / N.

For this reason, the S / N is deteriorated if the high spatial resolution and the narrowing of the optical band are attempted in this state, and therefore the S / N in the photodetector mounted on the artificial satellite is deteriorated.
In order to improve N, IMC (Image Motion Compensatio
(n: image motion compensation) is performed to achieve high spatial resolution and narrow optical band.

FIG. 6 shows an explanatory diagram of the operation of correction by IMC. The artificial satellite 31 detects light while moving at a constant speed in the direction of arrow C ₂ . In this case, the time t ₁ ~t same position P ₁ in _3, the time t ₄ ~t same position P ₂ at _6,
Light from the time t ₇ ~t ₉ in the same position P ₃ is controlled the light sensing unit to be incident on the light receiving surface of the mounted photodetector.

According to the IMC correction, the same position P ₁ ,
Since the light of P ₂ and P ₃ can be detected for a long time, the signal integration time t _int in the equation (1) can be lengthened, and thus the S / N can be improved.

FIG. 7 shows a block diagram of an example of a conventional photodetector. In order to obtain a linear image sensor 42 that converts light into an electrical signal, an interference filter 43 that supplies only light in a required band and supplies the linear image sensor 42 with a large S / N signal, IMC
(Image Motion Compensation) The mirror 44, the condenser lens 45 for condensing the incident light, and the drive device 46 for rotating the IMC mirror 44 in the direction of the arrow D to perform the IMC operation are included.

The light from the image pickup object 47 is condensed by the condenser lens 45, then enters the IMC mirror 44, is reflected by the IMC mirror 44, and is cut by the interference filter 43 to eliminate unnecessary high-frequency light. It is supplied to the linear image sensor 42.

As described above, in the conventional photodetector 41, the IMC mirror 44 is provided on the optical path, and the IMC correction operation is performed by controlling the angle of the IMC mirror 44.

[0013]

However, in the conventional photo-detecting device of this type, it is necessary to form an optical path extending through the IMC mirror to the photo-detector, and therefore the optical path becomes long and miniaturization is required. There are problems that it is difficult and the cost of the IMC mirror is increased.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a photodetector capable of performing IMC correction without an IMC mirror.

[0015]

According to the present invention, while moving relative to a detection target, light in a predetermined band of light from the detection target is supplied to a light detection unit through a filter for detection. In a light detection device for detecting light from an object, controlling the inclination of the filter with respect to the light detection means,
The filter drive control unit controls the light detection position of the light detection unit by controlling the refraction of light from the detection target.

[0016]

The light from the object to be detected is refracted by the filter by driving and controlling the inclination of the filter for supplying the light in the predetermined band among the light from the object to be detected to the light detecting means. Control the light detection position of.
Therefore, it is not necessary to separately provide a means for controlling the light detection position of the light detection means on the optical path. Therefore,
The optical path in the device can be shortened.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a block diagram of an embodiment of the present invention. The light detection device 1 of this embodiment is used for remote sensing by an artificial satellite, for example.

The photodetector 1 mainly includes a condenser lens 2 for condensing incident light, an interference filter 3 for transmitting light in a required band from the light condensed by the condenser lens 2, and an interference filter 3
It is composed of a drive unit 4 for driving the optical detector 4 and a photodetector 5 for converting the light transmitted through the interference filter 3 into an electric signal corresponding to the amount of light.

The condenser lens 2 condenses the incident light from the image pickup object 10 on the light receiving surface 5a of the photodetector 5. The interference filter 3 is arranged between the condenser lens 2 and the photodetector 5 and transmits light in a required band and cuts light in other bands. At this time, the band of the transmitted light is determined by the material forming the interference filter 3, sapphire glass or the like is used to transmit the visible light, and silicon (Si) -based or the like is used to transmit the infrared light. Germanium (Ge)
A system glass material is used.

The interference filter 3 is held by the drive unit 4 so as to be rotatable in the arrow A direction. The drive unit 4 is the interference filter 3
A piezoelectric element 7 for swinging the interference filter 3 at a predetermined frequency in the direction of arrow A, and a drive circuit 8 for supplying a drive signal to the piezoelectric element 7. The frame 6 is fixedly provided with respect to the photodetector 4, receives the rotating shaft 9 fixed to the end surface of the interference filter 3, and rotates the interference filter 3 around the rotating shaft 9 in the arrow A direction. Hold freely.

The piezoelectric element 7 includes a frame 6 and an interference filter 3.
And is oscillated in the direction of arrow B in accordance with the drive signal supplied from the drive circuit 8 to drive the interference filter 3 in the direction of arrow A.
Rotate in the direction. As the interference filter 3 rotates, the interference filter 3 tilts with respect to the photodetector 5, refracts the incident light L, and receives the incident light L on the light receiving area 5a of the photodetector 5.
The incident position on is displaced.

The drive circuit 8 is composed of an oscillating circuit or the like, generates a drive signal having a frequency according to the spatial resolution to be obtained and the moving speed of the artificial satellite, and supplies it to the piezoelectric element 7.

The photodetector 5 is composed of a line image sensor or the like, a plurality of light receiving elements 5b are arranged in a line, and the image pickup object is read line by line to form an image thereof. The light receiving element 5b is made of a material capable of efficiently converting the light in the band transmitted through the interference filter 3 into an electric signal, and when detecting infrared light, mercury-cadmium-tellurium (HgCdTe) or the like is used. A PN junction is formed of a compound semiconductor.

The optical detecting device 1 having the above-mentioned structure is an artificial satellite 31.
It is mounted on the board and moves in the direction of arrow C ₂ to detect light.

2 and 3 are explanatory views of the operation of an embodiment of the present invention. When the piezoelectric element 7 is displaced in the direction of the arrow B ₁ , the interference filter 3 is rotated about the rotation shaft 9 in the direction of the arrow A ₁ , and the interference filter 3 is inclined as shown in FIG. As shown in FIG. 3A, the optical axis L _A is displaced in the direction of arrow C ₁ .

When the piezoelectric element 7 is not displaced, the interference filter 3 is held horizontally as shown in FIG. 2 (B), and the optical axis L _B is displaced as shown in FIG. 3 (B). Absent.

When the piezoelectric element 7 is displaced in the direction of the arrow B ₂ , the interference filter 3 moves the arrow A ₂ about the rotation shaft 9 as a center.
Rotating in the direction, the interference filter 3 is tilted as shown in FIG. 2C, and the optical axis L _C is displaced in the arrow C ₂ direction.

At this time, the deviation of the optical axis L is caused by the interference filter 3
It is determined by the refractive index and tilt angle of.

FIG. 4 shows an operation explanatory diagram of the interference filter 3.
You The interference filter 3 is set to the time t shown in FIG.₁~ T₉Corresponding to
Then, as shown in FIG. 4, tilting it as shown in FIG.
Time t₁~ T₃At the same position P₁The light of the photo detector
5 to the light-receiving surface 5a at time t_Four~ T₆At the same position
P₂Of light is incident on the light-receiving surface 5a of the photodetector 5 at time t
₇~ T₉At the same position P₃Light of the light detector 5a of the photodetector 5
Can be incident on.

Thus, in this embodiment, the interference filter 3
Is tilted, and the light is displaced by the refractive index thereof to perform IMC. Therefore, an IMC mirror or the like is unnecessary.

As described above, according to this embodiment, the operation of the IMC as shown in FIG. 6 can be performed without the unnecessary structure of the IMC mirror or the like, and the SN ratio S / N can be improved.

Therefore, the SN ratio can be improved with a simple structure, the factors of failure and defects and the cost can be reduced, and the optical path of the incident light can be shortened, and the overall size can be reduced.

In this embodiment, the light detecting device mounted on the artificial satellite has been described, but the present invention is not limited to this, and the point is that the light is detected while moving relatively to the detection target. However, it may be configured so that the detection target side moves on the contrary.

Further, although the linear image sensor is used as the photodetector 5 in this embodiment, the invention is not limited to this.
A configuration using a photodetector using an area array image sensor is also conceivable.

[0035]

As described above, according to the present invention, the IMC operation can be performed by inclining the filter by the driving means and shifting the optical axis by the refractive index of the filter. The IMC operation can be performed with a simple configuration without unnecessary configuration, and the factors of failure and defects can be reduced and the cost can be reduced. Moreover, since the optical path of incident light can be shortened, the size of the device can be greatly reduced. Has features.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an output drive signal waveform diagram of the drive circuit according to the embodiment of the present invention.

FIG. 3 is an operation explanatory diagram of the embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of the embodiment of the present invention.

FIG. 5 is a diagram for explaining remote sensing by an artificial satellite.

FIG. 6 is a diagram illustrating the operation of the IMC.

FIG. 7 is a configuration diagram of a conventional example.

[Explanation of symbols]

 1 Photodetector 2 Condensing lens 3 Interference filter 4 Photodetector 5 Drive part 6 Frame 7 Piezoelectric element 8 Drive circuit

Claims (2)

[Claims] 1. The light from a detection target (10) is supplied to a light detection means (5) through a filter (3) through a filter (3) to detect the light from the detection target (10). In the photodetection device, the filter (3) is driven to rotate and the filter (3) is rotated.
A filter drive control means (4) for controlling the light detection position of the light detection means (5) by controlling the inclination of the light detection means (5) with respect to the light detection means (5). An optical detection device having. 2. The light detection means (5) is configured to detect light while moving relative to the detection target, and the filter drive control means (4) is configured to detect the light detection means (5). 5) The light detection positions (P ₁ , P ₂ , P ₃ ) of the filter (3) are set to be the same for a predetermined time (t _{1 to} t ₃ , t _{4 to} t ₆ , t _{6 to} t ₉ ). The photodetector according to claim 1, wherein the inclination is controlled.